This invention relates to an improved rangefinder system for a single reflex type photographic or cinematographic camera. More particularly, the invention relates to a dichroic rangefinder wherein the viewed image of an object is caused to be chromatically fringed when an objective lens is not focused on object, and wherein the chromatically distinct images are made coincident and therefore become neutral when the objective lens is focused. A reflex type rangefinder system which provides chromatically distinguishable images in viewfinder when the objective lens is not focused on the object is known as described in U.S. Pat. No. 3,618,498. The rangefinder system described in U.S. Pat. No. 3,618,498 provides a plano parallel prism as a beamsplitter, with one surface having a dichroic coating and another surface having a totally reflecting coating so to form the natural colored image in viewfinder when objective lens is in focus on the object and to form chromatically colored images in viewfinder when objective lens is out of focus.
The rangefinder system for a single reflex type viewfinder is also known as described in U.S. Pat. No. 3,696,724 wherein a pair of mirrors is provided in the lens system for directing light to the viewfinder. The two-mirror rangefinder system as explained in U.S. Pat. No. 3,696,724 can be used with non-afocal, non-collimated light rays by adjusting the positions of said mirrors relative to each other such that the images can coincide in viewfinder when the lens is in focus. Moreover, such two-mirror rangefinder systems can be made to have accuracy greater than found in rangefinders with prisms for beamsplitting. In the prior art two-mirror system the viewfinder images are not formed chromatically when the lens is out of focus; therefore, the chromatic effect of the U.S. Pat. No. 3,618,498 for dichroic beamsplitters cannot be expected when focusing.
The present invention offers an improved rangefinder system wherein the chromatically distinguishable viewfinder images are formed within the more accurate two-mirror rangefinder; thus, the optical elements are used more effectively.
Therefore, it is an object of this invention to provide a new and improved rangefinder system.
It is also an object of this invention to provide a dichroic dual beam rangefinder suitable for use in a single lens reflex camera.
It is another object of this invention to provide a dual beam rangefinder system including a pair of dichroic mirrors located to intersect light rays peripheral to the film image to permit chromatic light to reach the rangefinder and the maximum amount of light to reach the film.
It is a further object of this invention to provide adjustable mirrors to compensate for converging or diverging light coming from the zoom lens.